Process

ABSTRACT

A process for the manufacture of a useful product from carbonaceous feedstock of fluctuating compositional characteristics, comprising the steps of: continuously providing the carbonaceous feedstock of fluctuating compositional characteristics to a gasification zone; gasifying the carbonaceous feedstock in the gasification zone to obtain raw synthesis gas; recovering at least part of the raw synthesis gas from the gasification zone and supplying at least part of the recovered raw synthesis gas to a partial oxidation zone; equilibrating the H2:CO ratio of the raw synthesis gas in the partial oxidation zone to obtain equilibrated synthesis gas; recovering at least part of the equilibrated synthesis gas from the partial oxidation zone and treating the gas to remove impurities and generate a fine synthesis gas; and converting the optionally adjusted fine synthesis gas into the useful product in a further chemical reaction requiring a usage ratio.

TECHNICAL FIELD

The present invention concerns a chemical engineering process for theproduction of useful products, for example synthetic fuels, from wastematerials and/or biomass in a manner which improves efficiency andreduces the complexity of the process in comparison with conventionalprocesses of the type.

BACKGROUND

It is widely known in the art to manufacture useful products such assynthetic fuels from waste materials and/or biomass. We may refer tosuch manufacturing methods as WTL (Waste-to-Liquids) and BTL(Biomass-to-Liquids) processes.

Typical WTL and BTL processes involve the gasification by steamreforming of waste or biomass feedstock to produce a raw synthesis gaswhich may then be treated and purified in various ways before entering achemical reaction train to generate a useful product.

In the case of the useful product being a synthetic fuel, the chemicalreaction train will typically comprise a Fischer-Tropsch (FT) reactor.The FT process is widely used to generate fuels from carbon monoxide andhydrogen and can be represented by the equation:

(2n+1)H₂ +nCO→C_(n)H_(2n+2) +nH₂O

The so-called usage ratio is an indication of the required stoichiometryin the chemical reaction train. For an FT process the usage ratioapproximates ideally to 2 when n is a large number in the aboveequation. For example when n=100 the ratio is 2.01. It will beappreciated that in a complex reaction network, side reactions may occurin which case the overall usage ratio and the primary reactionstoichiometry may not be synonymous and further both of these can bedifferent from the ratio of reactants made available for the reaction.For example, in the case of FT the usage ratio in reality is typicallyin the range of 2.04 to 2.14, while the H₂:CO ratio in the feed can varysignificantly.

To date, there appears to have been little consideration given as to howthe feed H₂:CO ratio may be controlled below the usage ratio to increaseefficiency and reduce complexity in an otherwise satisfactory WTL or BTLprocess.

WTL and BTL processes are very well known in the art and certainprocesses have been considered for the production of fuel from sourcessuch as municipal and biomass waste.

For example, WO2017011025A1 and WO2017039741A1 concern systems forproducing high biogenic carbon concentration Fischer-Tropsch (F-T)liquids derived from municipal solid wastes (MSW), and a high biogeniccontent fuel derived from renewable organic feedstock sources.

EP2350233A1 relates to a method for producing liquid hydrocarbonaceousproduct from solid biomass, the method comprising gasifying solidbiomass to produce raw synthesis gas, conditioning the raw synthesis gasto obtain purified synthesis gas and subjecting the purified gas to aFischer-Tropsch synthesis.

WO2018026388 describes converting one or more carbon-containingfeedstocks into hydrocarbons.

US20190118157A1 relates to a synthesis gas production method in whichthe ratio of product gas components (both H₂:CO and CO:CO₂) iscontrolled and adjusted by substoichiometric (partial) oxidation andsubsequent oxidation of a raw synthesis gas. The disclosure suggests tocombine product gas from a partial oxidation unit and from a gasifierand to react the combined stream with an oxygen-containing gas togenerate a lower component ratio than either the of the product gasesfrom the partial oxidation unit or the gasifier.

EP3381997A1 and EP2694432A2 appear primarily concerned with the 00:002ratio in synthesis gas production and mention H₂:CO ratio only inpassing.

EP2694624B1 is similarly preoccupied with the 00:002 ratio.

The significance of the H₂:CO ratio is recognised in EP2530136A1 whichdiscloses that a gasifier operated at 700 to 950° C. conventionallyproduces a H₂:CO ratio of about 0.5 to 1.4 depending on feedstock. Thisdocument teaches recovering from the Fischer-Tropsch reactor an off-gascomprising hydrocarbons, separately producing hydrogen from thosegaseous hydrocarbons and feeding at least a part of the thus-producedhydrogen into the clean synthesis gas in order to increase thehydrogen-to-carbon monoxide ratio of said clean synthesis gas.

Much consideration of H₂:CO ratios is also provided in EP2865732A, whichfocuses on mixing raw synthesis gas from a biomass gasifier and ahydrogen-rich gas to yield a mixed gas, wherein a volume ratio of thehydrogen-rich gas to the raw synthesis gas is between 0.7 and 2.1 andthen generating from that raw synthesis gas a fine synthesis gas havinga H₂:CO volume ratio of between 1.8 and 3.0.

Fischer-Tropsch is by no means the only synthesis to benefit fromconsideration of component gas ratios. For example, EP1934311A1discusses usage ratios in terms of “stoichiometric number” (SN) andteaches the adjustment of SN to a suitable value for use in methanolsynthesis.

It is also known, for example from Taherzadeh, Mohammad & Chandolias,Konstantinos & Richards, Tobias. (2018). CombinedGasification-Fermentation Process in Waste Biorefinery.10.1016/6978-0-444-63992-9.00005-7 that different feedstocks ongasification generate synthesis gas of different composition, includingas regards the H₂:CO ratio.

US2015/0299589 describes a method of processing synthesis gas to improvethe quality of the synthesis gas by using a water gas shift reaction toincrease the molar ratio of hydrogen to carbon monoxide (H₂:CO).

WO2008/017741 describes a method of producing liquid hydrocarbons from aheavy charge such as biomass, coal, lignite, or heavy petroleum residuecomprising partial oxidation of the heavy charge, producing a syntheticgas SG1, with H₂/CO ratio of <1, steam reforming a light chargecomprising hydrocarbons having at most four carbon atoms, to produce asynthetic gas SG2 with H₂/CO ratio>3, a Fischer-Tropsch conversion of asynthetic gas SG into liquid hydrocarbons, mixture of at least one partof SG1 and at least one part of SG2, in proportions such that SG has aH₂/CO ratio of between 1.2 and 2.5.

US2009/0012188 describes a process of producing liquid hydrocarbons froma feedstock that comprises at least one elementary feedstock from thegroup of biomass, coal, lignite, petroleum residues, methane, andnatural gas, comprising at least one stage a) for gasification of thefeedstock by partial oxidation and/or steam reforming to produce asynthesis gas SG; a stage b) for separating CO₂ from SG and a portion ofthe effluent of the subsequent stage c); the mixing of a portion of theCO₂ that is separated with a gas of an H₂/CO ratio of more than 3; astage c) for partial conversion with hydrogen, thermal orthermocatalytic, of the CO₂ that is present in said first mixtureaccording to the reaction: 002+H₂->CO+H₂O in a specific reaction zonethat is separated from said gasification zone or zones; a stage d) forFisher-Tropsch synthesis on a synthesis gas that comprises at least aportion of SG and at least a portion of the CO that is produced by theconversion of CO₂ into hydrogen.

U.S. Pat. No. 4,110,359 describes a continuous process forsimultaneously producing a stream of cleaned purified synthesis gashaving a mole ratio H₂:CO in the range of 2 to 12 and a separate streamof CO-rich gas.

WO2008/010994 describes a method for controlling a synthesis gascomposition obtained from a steam methane reformer (SMR) that obtainsits feedstock as product gas directly from a steam hydro-gasificationreactor (SHR).

It would appear that none of these documents provides a satisfactorymeans for controlling the H₂:CO ratio in the feed to be below the usageratio to increase efficiency and reduce complexity in an otherwisesatisfactory WTL or BTL process. In particular, none contain anysatisfactory teaching as to how to handle compositionally fluctuatingfeedstocks.

The object of the present invention is to provide an improved processfor manufacturing a useful product such as synthetic fuel from wastematerials and/or biomass, in which the H₂:CO ratio in the feed iscontrolled to be below the usage ratio to increase efficiency and reducecomplexity in comparison with conventional such processes.

SUMMARY OF INVENTION

According to the present invention there is provided a process for themanufacture of a useful product from waste materials and/or biomass byproducing a synthesis gas from a feedstock material and subsequentlyconverting the synthesis gas to a useful product in a conversion processhaving a particular H₂:CO in relation to the usage ratio, the processcomprising:

selecting for a first period of time a first carbonaceous feedstockmaterial comprising or derived from waste materials and/or biomass;

gasifying in a gasification zone at least part of the first carbonaceousfeedstock material to produce a first raw synthesis gas having a firstraw synthesis gas H₂:CO ratio;

partially oxidising in a partial oxidation zone at least part of thefirst raw synthesis gas to produce a first equilibrated synthesis gashaving a first equilibrated synthesis gas H₂:CO ratio controlled to bebelow the usage H₂:CO ratio of the conversion process;

treating at least part of the first equilibrated synthesis gas to removeimpurities and generate a first fine synthesis gas; and

subjecting at least part of the first fine synthesis gas to conversionprocess reaction conditions effective to produce a useful product;

selecting for a second period of time a second carbonaceous feedstockmaterial derived from waste materials and/or biomass, the secondcarbonaceous feedstock being different in its compositionalcharacteristics from the first carbonaceous feedstock;

gasifying in the gasification zone at least part of the secondcarbonaceous feedstock material to produce a second raw synthesis gashaving a second raw synthesis gas H₂:CO ratio;

partially oxidising in the partial oxidation zone at least part of thesecond raw synthesis gas to produce a second equilibrated synthesis gashaving a second equilibrated synthesis gas H₂:CO ratio also controlledto be below the usage H₂:CO ratio of the conversion process;

treating at least part of the second equilibrated synthesis gas toremove impurities and generate a second fine synthesis gas;

and

subjecting at least part of the second fine synthesis gas to conversionprocess reaction conditions effective to produce a useful product;

wherein the second raw synthesis gas H₂:CO ratio is different from thefirst raw synthesis gas H₂:CO ratio by a percentage ±x and wherein thesecond equilibrated synthesis gas H₂:CO ratio is the same as the firstequilibrated synthesis gas H₂:CO ratio or different from the firstequilibrated synthesis gas H₂:CO ratio by a percentage ±y, y being alower percentage than x.

Typically x is a percentage in the range of from about 1 to about 300.

Typically y is a percentage in the range of from 0 to about 20.

In the process of the invention y is preferably considerably lower thanx, for example at least about 10% lower, preferably at least about 25%lower, more preferably at least about 40% lower and most preferably atleast about 50% lower.

The process may comprise adjusting the H₂:CO ratio of at least part ofthe first equilibrated synthesis gas to generate an adjusted firstequilibrated synthesis gas having an adjusted H₂:CO ratio.

The process may comprise adjusting the H₂:CO ratio of at least part ofthe first fine synthesis gas to generate an adjusted first finesynthesis gas having an adjusted H₂:CO ratio.

The process may comprise adjusting the H₂:CO ratio of at least part ofthe second equilibrated synthesis gas to generate an adjusted secondequilibrated synthesis gas having an adjusted H₂:CO ratio.

The process may comprise adjusting the H₂:CO ratio of at least part ofthe second fine synthesis gas to generate an adjusted second finesynthesis gas having an adjusted H₂:CO ratio.

The process of the invention is therefore concerned with thepracticality of generating consistently and efficiently useful productsfrom variable carbonaceous feedstocks. For example, the feedstock canvary between biomass and waste. Even within the waste feedstock,material composition can vary significantly with regards to the amountof plastics, papers, food waste from batch to batch as well asseasonally. In a chemical process plant handling mixed feedstock streamsderived from waste and/or biomass there is inherent and significantvariability in the nature of the feedstock, in particular as regards theH₂:CO ratio evident in a raw synthesis gas generated from suchfeedstocks following gasification. Downstream processing of such rawsynthesis gas is freighted with difficulty because of the variablenature of such gas arising from different feedstocks at different timesin the production cycle. Wide variation in the raw synthesis gas H₂:COratio creates problems in consistently and efficiently adjusting thatratio for suitability with the selected downstream reaction train. Thisis particularly the case when the variability of feedstock is such as togive rise from time to time to H₂:CO ratios which are above thepreferred usage ratio of the downstream reaction. In that case theadjustment of H₂:CO ratio to generate fine synthesis gas must be madedownwardly, necessitating plant components effective for removing H₂from the raw synthesis gas by means of, for example, membrane separationunit as opposed to adding it (to increase the usage ratio) by means of,for example, the water gas shift reaction.

Accordingly, by “different in its compositional characteristics” we meanthat the compositional variation between the first and secondcarbonaceous feedstocks may be considerable over time—as between, forexample, different types of commercial or industrial waste or betweendifferent types of biomass, or even changing from biomass to commercialor industrial waste or a combination of both feedstocks—with varyingratio of the two components.

The first and second fine synthesis gas H₂:CO ratios are below the usageratio in the process of the invention. Any optional adjustment of atleast part of the first and/or second fine synthesis gas H₂:CO ratiosmay be effective to increase the H₂:CO ratio in the first and/or secondfine synthesis gas to a level at, above or nearer to the usage ratio. Itis generally preferred that any such adjustment should raise the H₂:COratio to a level at or nearer to the usage ratio. However, the usageratio can be exceeded if desired or acceptable, the main point beingthat any optional adjustment of the first and/or second fine synthesisgas H₂:CO ratios need only be effective to raise the H₂:CO ratio, not tolower it.

Consequently, when the reaction conditions effective to produce a usefulproduct include a desired ratio of H₂:CO in the feed it is required inaccordance with the invention that the equilibrated synthesis gas H₂:COratio serving as feed to the reaction be below the typical usage ratiofor the reaction before any optional adjustment.

By “in the feed” is meant the feed to the reaction train which generatesthe useful product—i.e. the first and/or second fine synthesis gasentering the reaction train, the H₂:CO ratio of which may be optionallyadjusted in an upwards direction to be at or nearer to the requiredusage ratio prior to passage into the reaction train.

In the process of the invention partial oxidation of the raw synthesisgas is effectively used to equilibrate the H₂:CO ratio to a large extenteven with respect to widely varying H₂:CO ratios in the raw synthesisgas arising from different feedstocks coming into the plant during anoperating cycle.

Accordingly, the invention also provides a process for the manufactureof a useful product from carbonaceous feedstock of fluctuatingcompositional characteristics, the process comprising the steps of:

continuously providing the carbonaceous feedstock of fluctuatingcompositional characteristics to a gasification zone;

gasifying the carbonaceous feedstock in the gasification zone to obtainraw synthesis gas;

recovering at least part of the raw synthesis gas from the gasificationzone and supplying at least part of the recovered raw synthesis gas to apartial oxidation zone;

equilibrating the H₂:CO ratio of the raw synthesis gas in the partialoxidation zone to obtain equilibrated synthesis gas;

recovering at least part of the equilibrated synthesis gas from thepartial oxidation zone;

optionally adjusting the H₂:CO ratio of at least part of theequilibrated synthesis gas to obtain adjusted equilibrated synthesisgas;

treating the optionally adjusted equilibrated synthesis gas to removeimpurities and generate a fine synthesis gas;

optionally adjusting the H₂:CO ratio of at least part of the finesynthesis gas to obtain adjusted fine synthesis gas; and

converting the optionally adjusted fine synthesis gas into the usefulproduct in a further chemical reaction with a particular usage ratio;

wherein the fine synthesis gas H₂:CO ratio is below the usage ratio andwherein any optional adjustment of at least part of the fine synthesisgas H₂:CO ratio is effective only to increase the H₂:CO ratio in thefine synthesis gas to a level at, nearer to or above the usage ratio;

wherein the H₂:CO ratio of the raw synthesis gas fluctuates duringoperation of the process as a result of the fluctuating compositionalcharacteristics of the carbonaceous feedstock by a percentage of ±x; and

the H₂:CO ratio of the equilibrated synthesis gas does not fluctuateduring operation of the process or fluctuates during operation of theprocess as a result of the fluctuating compositional characteristics ofthe carbonaceous feedstock by a percentage ±y, y being a lowerpercentage than x.

The further chemical reaction for converting the optionally adjustedfine synthesis gas into the useful product requires a desired feed ratioof H₂:CO and the equilibrated synthesis gas H₂:CO ratio may beconsistently below that desired feed ratio.

The useful product produced in the further chemical reaction byconversion of the optionally adjusted fine synthesis gas corresponds toa certain H₂:CO usage ratio and the equilibrated synthesis gas H₂:COratio may be consistently below that usage ratio.

The useful product produced in the further chemical reaction byconversion of the optionally adjusted fine synthesis gas corresponds toa certain H₂:CO usage ratio and the H₂:CO ratio in the optionallyadjusted fine synthesis gas may be consistently at or no more than 20%above or below that usage ratio.

As above, typically x is a percentage in the range of from about 1 to300 and y is typically a percentage in the range of from 0 to about 20.Also, as above, y is preferably considerably lower than x, for exampleat least about 10% lower, preferably at least about 25% lower, morepreferably at least about 40% lower and most preferably at least about50% lower.

Preferably the process of the invention is a continuous process whereincarbonaceous feedstock, of whatever nature provided it is derived fromwaste materials and/or biomass, is continuously fed to a gasificationzone for gasifying the feedstock. The process of the invention iseffective to equilibrate the H₂:CO ratio in the raw synthesis gasregardless of the compositional makeup of the carbonaceous feedstock.

DETAILED DESCRIPTION

The terms “raw synthesis gas”, “equilibrated synthesis gas”, “finesynthesis gas”, “shifted synthesis gas” and any other phrase containingthe term “synthesis gas” are to be construed to mean a gas primarilycomprising hydrogen and carbon monoxide. Other components such as carbondioxide, nitrogen, argon, water, methane, tars, acid gases, highermolecular weight hydrocarbons, oils, tars, volatile metals, char,phosphorus, halides and ash may also be present. The concentration ofcontaminants and impurities present will be dependent on the stage ofthe process and carbonaceous feedstock source. In particular, theconcentration of contaminants and impurities in the fine synthesis gasis lower, typically very considerably lower, than that in raw orequilibrated synthesis gas as the step of recovering at least part ofthe equilibrated synthesis gas from the partial oxidation zone andtreating the gas to remove impurities and generate a fine synthesis gas(i.e. clean-up step(s)) have yet to be performed at the stages of theinventive process at which both the raw synthesis gas and theequilibrated synthesis gas are generated.

The use of such terms to describe synthesis gas should not be taken aslimiting. The skilled person would understand that each of the terms isconstrued to mean a gas primarily comprising hydrogen and carbonmonoxide.

The carbonaceous feedstock may comprise at least one of woody biomass,municipal solid waste and/or commercial and industrial waste. Thecarbonaceous feedstock will have fluctuating compositionalcharacteristics that are dependent on the source and chemistry of thefeedstock used.

The carbonaceous feedstock may be in the form of relatively largepieces. The carbonaceous feedstock may be processed to remove oversizeditems, recyclates, highly halogenous plastics such as PVC, metals andinert items. These items cannot be converted into synthesis gas and/orare likely to a significant contaminant load (for example, the case ofhighly halogeneous plastics); therefore it is preferable to remove saiditems prior to gasification. These items may be recycled.

The carbonaceous feedstock may be reduced to a size suitable forgasification. For example, the carbonaceous feedstock may be comminuted,shredded or chipped prior to gasification.

In some embodiments, the carbonaceous material feedstock is biomass, forexample woody biomass feedstock. Example of suitable woody feedstock mayinclude tree length round wood, pulpwood thinnings, whole tree, limbs,branches, tops and/or waste wood.

In one embodiment, round wood is supplied to the plant as logs measuring5″ to 9″ diameter×15′ long. In another embodiment, wood chips aresupplied to the plant as 6-inch minus chips.

A shredder may be used to reduce the carbonaceous material to a suitablesize for the gasification zone. The shredder may reduce the size of thecarbonaceous material to particles of about 25 mm. At least about 85%,at least about 90%, at least about 95% by weight of the carbonaceousmaterial may be about 1 in³ or less in volume; depending on therequirements of the gasification technology deployed.

In another embodiment, the carbonaceous feedstock is waste material, forexample municipal solid waste and/or commercial and industrial waste.

The carbonaceous feedstock may comprise moisture. Preferably in thatcase, the carbonaceous feedstock is dried to at least some extent priorto gasification.

The carbonaceous feedstock may be conveyed to a dryer to reduce themoisture content to a suitable level. The moisture content may bereduced to less than about 20%, less than about 15% or less than about10% by weight. Preferably, the carbonaceous feedstock supplied to thegasification zone has a moisture content of at most 10% by weight;depending on the requirements of the gasification technology deployed.

When waste material (as mentioned above) is used as the carbonaceousfeedstock source, the feedstock may not need drying prior to enteringthe gasification zone. Waste material in this case may be fed directlyinto the gasifier after suitable pre-treatment to remove undesirablecomponents and comminute the feedstock to a size suitable for feedstockhandling.

The carbonaceous feedstock may be continuously fed into a gasificationzone.

The process of the invention obtains raw synthesis gas through gasifyingthe carbonaceous feedstock in a gasification zone. Gasification mayoccur in the presence of steam and oxygen. The gasification zone maycomprise a singular train, dual trains or multiple trains. Preferably,the gasification zone comprises more than one train to minimize impactof interruptions on the plant availability.

Three primary types of commercially available gasifiers are offixed/moving bed, entrained flow, or fluidized bed type. Thegasification zone may be an indirect gasification zone in whichfeedstock and steam are supplied to a gasification vessel which isindirectly heated. Alternatively, the gasification zone may be a directgasification zone in which feedstock, steam and an oxygen-containing gasare supplied to the gasification vessel and directly combusted toprovide the necessary heat for gasification. Also known in the art andsuitable for use in the process of the present invention are hybridgasifiers, and gasifiers incorporating partial oxidation units. In thatcase it will be understood that in the process of the invention thegasification zone and the partial oxidation zone may be separate zonesof a single vessel.

In one embodiment, the gasification zone comprises primarily anindirectly heated deep fluidized bed operating in the dry ash rejectionmode and a secondary gasifier for maximal conversion of the carbonaceousmaterial. In another embodiment, the gasification zone may comprise onlya primary indirectly heated fluidized bed.

The fluidised bed operating temperature may vary depending on thecompositional characteristics of the carbonaceous feedstock. Thefluidised bed operating temperature may be between about 400 and 1000°C., preferably between about 500 and 900° C., or more preferably betweenabout 600 to 800° C.

Such temperature ranges of the fluidised bed have been found to avoidany constituent ash from softening and forming clinkers with the bedmaterial.

The fluidized bed reactor may be preloaded with a quantity of inert bedmedia such as silica sand or alumina. The inert bed media may befluidized with superheated steam and oxygen. The superheated steam andoxygen may be introduced through separate pipe nozzles.

During gasification, the fluidized bed may undergo drying (ordehydration), devolatilization (or pyrolysis) and gasification. Somecombustion, water gas shift and methanation reactions may also occur.

It is desirable to have a pressure within the gasification zone thatminimises the need of compression in downstream processes. It istherefore preferable for the gasification zone to have a pressure of atleast about 3.5 bar if not higher, for example about 4 bar or more.Gasification zones operating at even much higher pressures such as 10bar or more are known in the art. Similarly, gasification zonesoperating at lower pressures, for example about 1.5 bar or less are alsoknown in the art. All are suitable for use in the process of the presentinvention.

The raw synthesis gas leaving the gasification zone may have an exittemperature of at least about 600° C., of at least about 700° C., or ofat least about 800° C. Preferably, the raw synthesis gas leaving thegasification zone has an exit temperature of from about 700° C. to about750° C.

The major products leaving the gasification zone are typically steam andraw synthesis gas comprised of hydrogen and carbon monoxide (CO) (theessential components of synthesis gas), carbon dioxide (CO₂), methane,and small amounts of nitrogen and argon. There may be additional tarssuch as benzene, toluene, ethyl benzene and xylene, higher hydrocarbons,waxes, oils, ash, soot, bed media components and other impuritiespresent.

Carbon dioxide, sulphur, slag and other by-products and impurities ofgasification may be amenable to capture, collection and reuse.

Cyclones may be used to remove undesirable solid materials from the rawsynthesis gas.

A tramp discharge system may be used to remove heavier contaminants fromthe bed material in operation of the gasification process.

Depending on the source of the feedstock used, the ratio of maincomponents and impurities present in the synthesis gas may vary, and thehydrogen to carbon monoxide ratio of the raw synthesis gas can varysubstantially. In particular, there will be greater fluctuation in thehydrogen to carbon monoxide ratio of the raw synthesis gas when wastefeedstock is used as the feedstock source due to the swings incompositional chemistry and variable moisture present. Biomass derivedfeedstocks can also vary according to type. For example, the gascomposition for Rice husk vs pine wood vs eucalyptus vs nut shells canresult in varying hydrogen to carbon monoxide ratios in the raw syngas(see Taherzadeh, Mohammad & Chandolias, Konstantinos & Richards, Tobias.(2018). Combined Gasification-Fermentation Process in Waste Biorefinery.10.1016/6978-0-444-63992-9.00005-7).

The hydrogen to carbon monoxide ratio in the feed and/or term “feedratio” is to be construed as the volume of hydrogen per volume of carbonmonoxide in the relevant feed stream.

The hydrogen to carbon monoxide usage ratio and/or term “usage ratio” isto be construed as the volume of hydrogen consumed in the reaction pervolume of carbon monoxide used in the further conversion process orchemical reaction (as mentioned in the statements of invention above) toproduce a useful product.

The presence of impurities can influence the processing conditions ofdownstream processes and further steps may be required to remove anyimpurities present. It is desirable to control the fluctuation of thehydrogen to carbon monoxide ratio in the raw synthesis gas according tothe invention to improve the overall performance, product yield andoptimisation when compared to conventional methods. The inventors havefound that controlling the hydrogen to carbon monoxide ratio fluctuationin the feed (raw synthesis gas) obviates the need to include additionalsteps downstream to optimise the process and remove impurities, which isdesirable.

Depending on the source of carbonaceous feedstock and the gasificationtechnology, the raw synthesis gas may comprise between about 3 and 40%carbon dioxide, in addition to other impurities and contaminants.

In order to obtain high-quality gas that is required for its use as afeedstock in downstream processes such as synthesis, the impurities needto be removed. Non-limiting examples of suitable synthesis includeFischer-Tropsch (FT) synthesis, ammonia synthesis and methanolsynthesis.

The hydrogen to carbon monoxide ratio of raw synthesis gas leaving thegasification zone may not be optimal for downstream synthesis reactions.Different synthesis reactions require different specific hydrogen tocarbon monoxide feed ratios;

therefore, it is desirable to influence the hydrogen to carbon monoxidefeed ratio to obtain maximal efficiencies and yield.

As a non-limiting example, it is desirable to increase the hydrogen tocarbon monoxide ratio of the raw synthesis gas when the downstreamsynthesis process is the Fischer-Tropsch reaction if it is significantlylower than the usage ratio.

The raw synthesis gas leaving the gasification zone may comprise asulphur concentration of less than about 500 ppm, less than about 400ppm, less than about 300 ppm, less than about 200 ppm. Preferably, theraw synthesis gas comprises a sulphur concentration of less than about200 ppm.

The concentration of sulphur in the raw synthesis gas will influence theprocess conditions that are employed downstream.

At least part of the raw synthesis gas from the gasification zone isrecovered and at least part of the recovered raw synthesis gas issupplied to a partial oxidation zone.

The raw synthesis gas in the partial oxidation zone will undergo partialoxidation reactions.

Conventional partial oxidation zones in the art are typically catalyticor non-catalytic (thermal).

The partial oxidation zone may partially combust tail gas from adownstream synthesis unit and/or natural gas with preheated oxygenand/or steam. The partial oxidation zone may comprise a burner toproduce a stream of hot oxygen.

The partial oxidation zone is effective sufficiently to raise thetemperature of the raw synthesis gas to convert at least some of anytars, naphthalene, higher hydrocarbons and methane present into carbonoxides, hydrogen and water.

The partial oxidation zone may operate at a temperature of least about1100° C., at least about 1200° C., at least about 1300° C. Preferably,the partial oxidation zone operating temperature is at least about 1300°C., most preferably in the range of from about 1200° C. to about 1350°C.

The partial oxidation zone may convert residual methane, naphthalene,higher hydrocarbons and tar components into carbon oxides, hydrogen andwater. Synthesis gas leaving the partial oxidation zone may be construedto be equilibrated synthesis gas.

The equilibrated synthesis gas leaving the partial oxidation zone willbe hot and may be cooled by generating steam. Generation of superheatedsteam and/or saturated high pressure steam is preferable to improveprocess efficiency. The cooled equilibrated synthesis gas may be passedthrough a venturi scrubber to remove any water and particulates such asash and soot. A caustic wash may be additionally used to remove anyother impurities such as ammonia, halides, nitrous oxides and remainingparticulates.

The partial oxidation zone may operate at a pressure slightly orsomewhat lower than that of the gasification zone (to avoid anyintermediate compression requirements). The partial oxidation zone mayoperate at a pressure of between about 2 and 3 bar for a gasificationprocess that operates around 3.5 bar, for example.

The inventors have surprisingly found the inclusion of a partialoxidation zone within the process according to the invention offersflexibility and gives the gasification zone the ability to the handle ofa wide range of feedstock with fluctuating compositionalcharacteristics. The inventors have unexpectedly found that the use of apartial oxidation zone is able to equilibrate the hydrogen to carbonmonoxide ratio of the raw synthesis gas in a fixed direction below theusage ratio, prior to optionally further adjusting the ratio with asingle or straightforward process step, for example, a water gas shiftreaction downstream of the partial oxidation zone but upstream of thereaction to generate a useful product or by adding hydrogen from othersources.

The inventors have unexpectedly found that the use of a partialoxidation zone according to the invention can equilibrate the hydrogento carbon monoxide ratio in raw synthesis gas obtained from gasificationof a wide variety of sources of carbonaceous feedstock to obtain a moreconsistent value below the usage ratio of the selected downstreamreaction to form a useful product. The partial oxidation zone has beenfound to equilibrate the H₂:CO ratio of the raw synthesis gas enteringthe partial oxidation zone to a fixed range below the usage ratio,regardless of the source of carbonaceous feedstock used. This isparticularly advantageous when waste and/or biomass feedstocks are useddue to the greater variability in chemical composition compared toconventional feedstocks, leading to a greater fluctuation in H₂:CO ratioof the raw synthesis gas.

For specific synthesis reactions, the H₂:CO ratio in the feed to thechemical reactor in which the synthesis takes place is required to be inwithin a desired range, typically lower than the usage ratio. The usageratio is dependent on the synthesis reaction conditions and the desiredproduct make.

As a non-limiting example, when a Fisher-Tropsch reaction is employed asthe reaction for generating a useful product, a ratio of H₂:CO in theoptionally adjusted fine synthesis gas is significantly above the usageratio will cause the reaction to run at an increased rate, which isundesirable as the increased rate of reaction may subsequently lead toan uncontrolled reaction resulting in a thermal runaway situation.

Alternatively, if the H₂:CO ratio in the optionally adjusted finesynthesis gas is significantly below the usage ratio, there is alikelihood of depletion of hydrogen towards the exit of the catalyst bedin the reaction zone in which the reaction to obtain a useful producttakes place, resulting in accelerated deactivation accompanied bypotential deposition of carbonaceous species, which is undesirable.

It is, therefore, highly important that the H₂:CO ratio in theoptionally adjusted fine synthesis gas be in a desired range, below orat or above, but not significantly above or below, the usage ratio. By“not significantly” is meant not more than 20%.

Depending on the feedstock and the variation in feedstock composition,the H₂:CO ratio in the raw synthesis gas (recovered from gasificationzone) can be either below or above this desired range (and usage ratio).The processing steps needed to bring this hydrogen to carbon monoxideratio in the desired range vary significantly with the direction of thedeviation. For cases where the H₂:CO ratio in the raw synthesis gas isbelow the desired range—a water gas shift reactor can be employed toincrease the hydrogen content of the stream. However, for the case wherethe H₂:CO ratio in raw synthesis gas is above the desired range—ahydrogen removal step such as using a membrane or pressure swingadsorption would have to be deployed. Given that these processing stepsare very different and require separate equipment, having a ratio ofH₂:CO in the raw synthesis gas in a single direction relative to thedesired range can result in significant operational flexibility andreduced capital costs in constructing plant to implement the process ofthe invention. For example, with seasonal or source based wastecompositional changes or a switch from biomass to waste as feedstock,the resulting H₂:CO ratio in the raw synthesis gas can change from belowdesired range to above the desired range and it would then be necessaryto alternate from one set of reaction equipment to another (as describedabove). This would increase operational complexity and would requireboth sets of equipment to be installed and configured to accept feedgas, which would add significant complexity to the plant and alsonecessitate additional expenditure in terms of the capital cost oflaying down the plant.

However, with the inclusion of the equilibration step afforded by thepartial oxidation zone in the process of the invention, the H₂:CO ratioin the equilibrated synthesis gas is forced to be below the desiredrange (and the usage ratio). Thus, the facility now needs only one setof equipment (for example, the water gas shift reactor mentioned above)in order to adjust the H₂:CO ratio in the equilibrated synthesis gas tothe correct desired range in the optionally adjusted fine synthesis gas.

The partial oxidation zone may also make the handling and removal ofnitrogen, sulphur and phosphorus species easier. By way of non-limitingexamples, the organic sulphur species may form COS and H₂S, the organicnitrogen species may form HCN and the phosphorus species may form P₂O₅which are easier to remove compared to their organic counterparts.

The partial oxidation zone may melt any ash present to form a slag. Theslag may be collected via a slag bath.

With the inventive process the following equipment may be selected forthe further processing of the equilibrated synthesis gas.

The equilibrated synthesis gas may be compressed. The compression ofsynthesis gas may occur after the synthesis gas has left the partialoxidation zone and has been cooled.

At least a part of the equilibrated synthesis gas from the partialoxidation zone may be passed through a Water Gas Shift (WGS) unit toobtain shifted synthesis gas and blended with the remaining equilibratedsynthesis gas to adjust the hydrogen to carbon monoxide ratio to thedesired range.

The term “water gas shift reaction” or “WGS” is to be construed as athermochemical process comprising converting carbon monoxide and waterinto hydrogen and carbon dioxide. The synthesis gas obtained after theWGS reaction may be construed to be shifted (i.e. adjusted) synthesisgas.

The presence of sulphur compounds is important when considering thechoice of WGS catalyst for the WGS reaction. Sulphur may be removed fromthe feed prior to WGS process or a sulphur tolerant WGS catalyst can beused (sour shift catalyst). Preferably, sulphur is removed from the feedprior to the WGS process.

In one embodiment, the synthesis gas entering the WGS unit isessentially a low sulphur gas (<0.1 ppmv) to enable a sweet shift. Thesynthesis gas entering the WGS unit may be equilibrated synthesis gas.

The process according to the present invention may further comprisesequentially removing ammoniacal, sulphurous and carbon dioxideimpurities from the raw synthesis gas.

The process of sequentially removing ammoniacal, sulphurous and carbondioxide impurities from the raw synthesis gas and recovering carbondioxide may occur prior to the WGS reaction. The resulting synthesis gasmay be construed to be desulphurised synthesis gas.

The removal of ammoniacal, sulphurous and carbon dioxide impurities maybe a physical or chemical absorption process.

In accordance with the present invention, sulphur may be removed inupstream processes. The equilibrated gas supplied to the water gas shiftunit is essentially a low sulphur gas.

The water gas shift reaction may use a sweet shift catalyst. The sweetshift catalyst may be a metal sulphide catalyst.

The physical absorption process may be a Rectisol™ process, a Selexol™process, or any similar solvent based physical absorption process.

In one embodiment, the physical absorption unit may be configured tooperate a dual stage process with two separate absorber columns thatcontact the synthesis gas stream with methanol comprising a commonmethanol regeneration system. The first absorber column may selectivelyremove sulphur and may use a CO₂ saturated solvent to minimise CO₂absorption in the sulphur removal column. The second absorber column mayrecover 002.

This technology is further described elsewhere; for example in FossilFuel Emissions Control Technologies, Bruce Miller, 2015.

Carbon dioxide may be recovered in substantially pure form. The recoveryof CO₂ may follow the WGS reaction.

The inventors have found that the use of a WGS reaction according to theinvention is able to adjust the hydrogen to carbon monoxide ratio of thesynthesis gas entering the WGS unit to a desired ratio (below the usageratio) according to the intended reaction.

The synthesis gas has already been equilibrated in the partial oxidationzone prior to entering the WGS shift unit; therefore the fluctuation ofthe hydrogen to carbon monoxide ratio in the synthesis gas has alreadybeen substantially reduced. The resulting shifted synthesis gasoptionally blended with the remainder of the equilibrated synthesis gas(forming the optionally adjusted fine synthesis gas) therefore obtains adesired hydrogen to carbon monoxide ratio specific to the intendedsynthesis, with an even reduced fluctuation.

The WGS reaction converts carbon monoxide and water into hydrogen andcarbon dioxide in the presence of (high pressure superheated) steam.

At least a portion of the equilibrated synthesis gas and/or rawsynthesis gas may be bypassed without subjecting said synthesis gas to aWGS reaction, thereafter, combining said shifted and bypassed gas intooptimal proportions to obtain the desired hydrogen to carbon monoxidefeed ratio in the optionally adjusted fine synthesis gas. The proportionof gas bypassed will vary depending on the desired ratio of thesynthesis reaction downstream and the severity of the shift reaction.Controlling the proportion of bypassed gas sent to the reactors helps inobtaining specific hydrogen to carbon monoxide feed ratios.

As a non-limiting example, it is desirable to increase the hydrogen tocarbon monoxide ratio of the equilibrated synthesis gas when wanting tosupply optionally adjusted fine synthesis gas to a Fisher-Tropschreactor.

The optionally adjusted fine synthesis gas has a hydrogen to carbonmonoxide ratio of 2.00±10%, preferably ±5%, ±2%, ±1%, ±0.5%, ±0.1%, or±0.05%.

Hydrogen may be recovered from the shifted synthesis gas downstream ofthe water gas shift reaction.

At least a portion of the shifted synthesis gas may be sent to aHydrogen Recovery Unit (HRU). The HRU may utilize a Pressure SwingAdsorption (PSA) process to produce high purity hydrogen for differentuses. The high purity hydrogen may be used in upstream and/or downstreamprocesses. However, because of the equilibratory effect of the POx zonein the process of the invention, the installed size of this unit issignificantly smaller compared to that required for removal of hydrogenfrom the raw synthesis gas stream in order to adjust the H₂:CO ratio tothe desired range for the further chemical reaction. The offgas from HRUmay be used as a fuel gas to reach required combustion temperatures inthe incinerators. It may be noted that in the process of the inventionany HRU which is present may be utilised to generate hydrogen forvarious uses, either off- or on-plant, but it is not necessary toconfigure the plant to remove hydrogen from any synthesis gas for thepurpose, or solely for the purpose, of reducing the H₂:CO ratio in thesynthesis gas as it progresses downstream into a chemical reactor forgenerating a useful product, as explained above.

The high purity hydrogen from the HRU may be about at least 97%, atleast about 98%, and least about 99% pure, at pressure. Impurities thatare removed may include, but are not limited to, CO, CO₂, CH₄, N₂ andAr.

The upstream and/or downstream processes utilizing the recoveredhydrogen may include removal of at least one of the ammoniacal, orsulphurous or carbon dioxide impurities, catalyst regeneration ofsynthesis reactors and product upgrading.

The shifted synthesis gas from the WGS unit combined with bypassedsynthesis gas may pass through an inlet filtration system, for examplean inlet guard bed, prior to the synthesis unit. The inlet guard bed maybe a sulphur guard bed. The inlet guard bed may operate in a lead-lagconfiguration to remove residual traces of contaminants such as hydrogensulphide, phosphorus, COS, arsenic, chlorides and mercury from thesynthesis gas. The lead bed may remove any contaminants present and thelag may serve as a safeguard for when the lead bed breaks through.

The synthesis gas leaving the guard bed may be construed as optionallyadjusted fine synthesis gas.

Optionally adjusted fine synthesis gas may be converted into a usefulproduct.

The useful product may comprise liquid hydrocarbons. The liquidhydrocarbons may be sustainable liquid transportation fuels.

The useful product may be produced by subjecting at least part of theoptionally adjusted fine synthesis gas to a Fischer-Tropsch synthesisunit.

At least a portion of the synthesis gas may be fed into a synthesisunit. Non-limiting examples of suitable synthesis includeFischer-Tropsch, ammonia synthesis, methanol synthesis or alcoholsynthesis.

Synthesis reactions require specific hydrogen to carbon monoxide ratioin feed gas (“desired ratio”) for optimum performance to meet processrequirements, maximise conversion and product yield. As a non-limitingexample, the Fischer-Tropsch synthesis feed may have a hydrogen tocarbon monoxide ratio of about 2. This desired ratio is typically lowerthan the usage ratio. As a non-limiting example, the Fischer-Tropschsynthesis usage ratio may be in the 2.04-2.14 range, typically about2.1.

According to the embodiment relating to Fischer-Tropsch synthesis, theoptionally adjusted fine synthesis gas may be fed into a FT reactor.

The synthesis unit may be a FT unit comprising FT reactors. The FTreactors may comprise microchannels. Filters may be used to remove anyparticulates.

The FT reactor may convert at least part of the carbon monoxide andhydrogen of the optionally adjusted fine synthesis gas into mainlylinear hydrocarbons.

The Fischer-Tropsch synthesis unit may convert the optionally adjustedfine synthesis gas into liquid hydrocarbons.

The conversion of synthesis gas into liquid hydrocarbons is conducted inthe presence of a catalyst. The chain length distribution will bedependent on the properties of the catalyst used and the operatingconditions.

Fischer-Tropsch reactions are exothermic and release heat that must beremoved to keep the temperature of the reaction approximately constant.Localised high temperatures in the catalyst bed have been found toadversely affect the FT product mix, yield and potentially reducecatalyst life. Therefore, it is desirable to keep the temperatureconstant.

The temperature may be controlled by varying pressure of a steam drumassociated with the FT reactor used in conjunction with circulatingcooling water.

The operating temperature for the FT synthesis may be between about 125and 350° C., between about 150 and 300° C., between about 170 and 250°C., between about 180 and 240° C. Preferably, the operating temperatureis between about 180 and 240° C. for a low temperature FT technology.

The catalyst may be a metal or compounded metal catalyst with a support.In one embodiment, the metal is cobalt. The support may be made fromsilica and/or titania.

The products that may be obtained in the FT synthesis, for example, saidhydrocarbons, may include heavy FT liquid (HFTL), light FT liquid(LFTL), FT process water, naphtha, and tail gas comprising of inerts aswell as uncondensed light hydrocarbons, typically C1 to C4. A part ofthe tail gas comprising of light hydrocarbons, C1 to C4 range, may berecycled back to the partial oxidation zone or sent to a fuel gassystem.

A part of the tail gas stream may be combined with the fresh synthesisgas prior to being fed to the FT reactors to maximize the utilization ofCO available in the synthesis gas. In such instances, A purge stream maybe used to prevent build-up of inert gases, such as CO₂ and CH₄, thatare produced in the FT reactors. The use of tail gas stream as a fueldescribed above would qualify as a purge stream as the gases leave theprocess loop.

It is desirable to upgrade the liquid hydrocarbons into a further usefulproduct.

The liquid hydrocarbons may be upgraded to make a further usefulproduct. At least part of the liquid hydrocarbons may be upgraded by atleast one of hydroprocessing, hydrotreating, product fractionation,hydrocracking and/or hydroisomerisation.

The FT liquid upgrading unit may produce high quality naphtha andSynthetic Paraffinic Kerosene (SPK). Other upgraded products may includegasoline, diesel and waxes. The unit may be configured as a recyclehydrocracker.

The further useful product may be a sustainable liquid transportationfuel or a gasoline blendstock. The transportation fuel or gasolineblendstock may be used for aviation and/or vehicles. The sustainableliquid transportation fuel may comprise high quality SPK. The gasolineblendstock may comprise naphtha.

The products formed by a process according to the present invention mayconstitute cleaner versions of fuels formed by conventional processes.

The fuel produced according to the present invention may improve airquality, with up to 90% reduction in particulate matter (soot) fromaircraft engine exhausts and almost 100% reduction in sulphur oxides.

The invention also provides a useful product produced by a process asdisclosed herein.

The invention also provides a process for the manufacture of apredetermined hydrocarbon product from a carbonaceous feedstock feed offluctuating composition, the process having a target usage ratio ofH₂:CO associated with the production of said predetermined hydrocarbonproduct, the process comprising:

a) gasifying the carbonaceous feedstock in a gasification zone to obtainraw synthesis gas having a percentage fluctuation ±x in its H₂:CO ratio;

b) equilibrating the raw synthesis gas to generate equilibratedsynthesis gas in an equilibration zone in which the H₂:CO ratio isadjusted towards said target ratio, the equilibrated synthesis gashaving a percentage fluctuation ±y in its H₂:CO ratio wherein y<x,

c) treating the equilibrated synthesis gas to remove impurities andgenerate a fine synthesis gas, and

d) converting the fine synthesis gas into the hydrocarbon product.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts a schematic diagram of a process applying conventionalteaching in the prior art for undertaking FT synthesis from multiplefeedstock sources or a feedstock source with variable composition. Thesection highlighted by the dashed area highlights steps which are notrequired for the process in accordance with the present invention.

FIG. 2 depicts a schematic diagram of the process according to thepresent invention.

Referring to FIG. 1 , prior art processes conventionally requiredifferent routes for the synthesis gas after gasification, depending onwhether the hydrogen to carbon monoxide ratio in the generated rawsynthesis gas is higher or lower than the usage ratio for the desiredreaction, in order to obtain synthesis gas suitable for the requiredsynthesis, which has been depicted as FT synthesis. Prior art processesare not able to handle varying hydrogen to carbon monoxide ratios in thefeed that are on either side of the usage ratio using the same processequipment and therefore require different routes before feedingoptionally adjusted fine synthesis gas streams to the FT synthesis unit.Comparing the schematic of FIG. 1 to FIG. 2 , the process according tothe present invention eliminates several stages that are required in theconventional prior art process, thus simplifying the overall process andprovides a process with a reduced number of stages.

The elimination of these stages is made possible due to the presence ofa partial oxidation zone which equilibrates the hydrogen to carbonmonoxide ratio in the raw synthesis gas leaving the gasification zone toa small window below the usage ratio, independent of the feedstockemployed. Therefore, it is not necessary to separate the processingsteps based on whether the hydrogen to carbon monoxide ratios in thefeed are lower or higher than usage ratios, as in the prior artprocesses, in order to obtain the desired ratio for an FT reaction. Thisis because the H₂:CO ratio in the equilibrated synthesis gas exiting thepartial oxidation zone will be homogenised and always lower than theusage ratio. The process according to the present invention is thereforebeneficial in providing a process that offers flexibility in relation tothe feedstock used and reduces the need for additional stagesdownstream. This can be seen in the Examples illustrated below.

FIG. 3 depicts a graph of the hydrogen to carbon monoxide ratio of theraw synthesis gas exiting the gasification zone and the equilibratedsynthesis gas exiting the partial oxidation zone in accordance with thepresent invention when different feedstock sources are used. FIG. 3 alsohighlights the typical hydrogen to carbon monoxide ratio of thesynthesis gas desired for a FT reaction and the typical usage ratioobserved in the FT reaction. The results demonstrate the equilibrationof usage ratio upon exiting the partial oxidation zone independent ofthe source of feedstock.

FIG. 4 depicts a graph of the mol % of CH₄ present in the synthesis gasexiting the gasification zone and the partial oxidation zone inaccordance with the present invention when different feedstock sourcesare used. The results demonstrate the significant reduction in CH₄present in the synthesis gas exiting the partial oxidation zone incomparison to the gasification zone, indicating that more of the carbonis captured and utilized in the process.

FIG. 5 depicts a graph showing the effect that the partial oxidationoperating temperature has on the hydrogen to carbon monoxide ratio andmol % of CH₄ in the equilibrated synthesis gas leaving the partialoxidation zone. The partial oxidation zone temperature may be used as alever to tune the methane slip and the hydrogen to carbon monoxide ratioin the equilibrated synthesis gas.

The invention will now be more specifically described with reference tothe following non-limiting examples.

EXAMPLES

Table 1 outlines different sources of feedstock compositions that wereused in accordance with the present invention to obtain synthesis gasused for a FT process.

The % moisture content of the feedstock after preliminary feedstockhandling and drying is also indicated.

TABLE 1 Feedstock Composition/% High (40%) Household Commercial plasticMoisture Ex waste waste Food Paper content waste Hardwood Pine content/%1 100 10 2 70 30 10 3 70 30 15 4 100 10 5 100 10 6 100 10 7 25 75 —

Examples 1 to 7 are all feedstocks for use in the process of theinvention.

Process

Each of Examples 1 to 7 are treated as follows:

The feedstock of each Example is initially processed by the removal oflarge contra-material, recyclates (e.g. metals, ferrous and non-ferrous)and inerts such as glass, stone and grit. The resulting treatedfeedstock is then comminuted and dried to a desired moisture content (inthis case 10%) to obtain Solid Recovered Fuel (SRF).

The SRF is supplied continuously at a pre-determined rate to a fluidisedbed gasification unit operated at a temperature of approximately 700°C., a pressure of approximately 2.2 barg and supplied with superheatedsteam to effect the gasification and produce a raw synthesis gas havinga first H₂:CO ratio.

The raw synthesis gas exits the gasifier and is supplied to anoxygen-fired partial oxidation reactor maintained at a temperature above1250° C. and supplied with all of the raw synthesis gas at generatedfrom the gasification step described above while adjusting the oxygenrate to achieve the target temperature. The partial oxidation reactionconverts residual methane and other hydrocarbons into synthesis gas andgenerates an equilibrated synthesis gas having a second H₂:CO ratio.

The resulting hot equilibrated synthesis gas is cooled (by generatingsuperheated and saturated high pressure steam) to a temperature below200° C. and is then routed through a primary gas cleanup unit where itpasses through a venturi scrubber to knock-out water and particulates(such as soot and ash), after which it is caustic-washed to removeammonia, halides (e.g. HCl), nitrous oxides and any remainingparticulates.

The synthesis gas is then compressed and routed through a secondary gascleanup and compression system in which acid gas (H₂S and CO₂) removalis effected by the Rectisol™ process using a methanol solvent which“sweetens” the synthesis gas.

The secondary gas cleanup process includes various guard beds to removematerials such as mercury, arsenic and phosphorus along with additionalsulfur polishing beds which serve as (FT) inlet guard beds.

A portion of the synthesis gas stream is passed through a Water GasShift (WGS) unit to adjust the hydrogen to carbon monoxide (H₂:CO) ratioin the total feedstream (to the desired ratio) as it recombines.

Optionally adjusted fine synthesis gas is sent to the FT microchannelreactors where, in the presence of a cobalt catalyst supported on asilica/titania support, it is converted into synthetic liquidhydrocarbons.

The synthetic FT liquids are hydrocracked, hydroisomerised and thenhydrotreated. Subsequently they are fractionated into LPG, naphtha andSPK.

Table 2 shows the usage ratio of the synthesis gas exiting thegasification and the partial oxidation zone (also depicted in FIG. 3 ).

TABLE 2 H₂:CO (mol/mol) Ex Gasification Zone Exit Partial oxidation ZoneExit 1 1.11 0.85 2 1.15 0.86 3 1.22 0.89 4 1.09 0.84 5 3.05 1.00 6 0.510.87 7 2.01 0.84

Table 3 shows the relative percentage variation between each pair of theExamples in the H₂:CO ratio at the gasification zone exit, calculate as(column/row-1). Negative numbers indicate a lower H₂:CO than one beingcompared with.

TABLE 3 Example 1 2 3 4 5 6 7 1 4 10 −2 175 −54 81 2 −3 6 −5 165 −56 753 −9 −6 −11 150 −58 65 4 2 6 12 180 −53 84 5 −64 −62 −60 −64 −83 −34 6118 125 139 114 498 294 7 −45 −43 −39 −46 52 −75

Table 4 shows the relative percentage variation between each of theExamples in the H₂:CO ratio at the partial oxidation zone exit,calculate as (column/row-1). Negative numbers indicate a lower H₂:COthan one being compared with.

TABLE 4 Example 1 2 3 4 5 6 7 1 X 1.2 4.7 −1.2 17.6 2.4 −1.2 2 −1.2 X3.5 −2.3 16.3 1.2 −2.3 3 −4.5 −3.4 X −5.6 12.4 −2.2 −5.6 4 1.2 2.4 6.0 X19 3.6 0 5 −15 −14 −11 −16 X −13 −16 6 −2.3 −1.1 2.3 −3.4 14.9 X −3.4 71.2 2.4 6.0 0 19 3.6 X

It will be seen in comparing each of Tables 3 and 4 that the percentagedifference between the H₂:CO ratios of each example compared to eachother example is consistently lower and in many cases very substantiallylower at the partial oxidation exit than it is at the gasification zoneexit.

It can be seen from the results in Tables 3 & 4 above and FIG. 3 thatthe hydrogen to carbon monoxide ratio of the raw synthesis gas exitingthe gasification zone varies substantially depending on the feedstockemployed. Different syntheses require specific desired ratios forhydrogen to carbon monoxide in feed. Also illustrated in FIG. 3 are thetypical desired H₂:CO feed ratio of the synthesis gas and the usageratio for a FT reaction.

It can also be seen from the results that the equilibrated synthesis gasleaving the partial oxidation zone has significantly reduced thevariability in the hydrogen to carbon monoxide ratio for the differentfeedstock compositions compared to the hydrogen to carbon monoxideratios of the raw synthesis gas exiting the gasification zone.Therefore, the use of a partial oxidation zone in accordance with thepresent invention equilibrates the hydrogen to carbon monoxide ratio ofthe synthesis gas exiting partial oxidation zone independent of thesource of feedstock used and irrespective of the hydrogen to carbonmonoxide ratio of the raw synthesis gas exiting the gasification zone(and subsequently entering the partial oxidation zone).

The synthesis gas leaving the partial oxidation zone may be fed into aWGS reactor prior to the FT reaction in accordance with the presentinvention to obtain a desired ratio for hydrogen to carbon monoxidewithin the highlighted range consistent with a typical FT feed ratiothat is below the usage ratio. The WGS reaction is used to increase thehydrogen to carbon monoxide ratio of the synthesis gas exiting thepartial oxidation zone to fall within the typical FT synthesis feedrange. Thus, without the partial oxidation zone in the present inventionExamples 5 and 7 would not fall within such values and would requirealternative treatment to reduce the hydrogen to carbon monoxide ratio.

Table 5 shows the % mol content of CH₄ exiting the gasification andpartial oxidation zone in accordance with the present invention. As canbe seen by the results, there is a significant reduction in the presenceof CH₄ leaving the partial oxidation zone compared to the gasificationzone. The reduction in CH₄ impurities is important for increasing thecapture and recovery of carbon from the feedstock to the product. Thepartial oxidation zone converts residual methane into carbon oxides.

TABLE 5 CH₄ (% mol) Ex Gasification Zone Exit partial oxidation ZoneExit 1 7.9 0.02 2 7.8 0.03 3 7.4 0.02 4 7.1 0.01 5 3.0 0.01 6 10.2 0.047 5.2 0.15

The H₂:CO in the gas exiting the partial oxidation zone can beinfluenced by the operating temperature of the partial oxidation.However, thermal partial oxidation is typically operated at temperaturesabove 1200° C. to minimize the CH₄ slip. The syngas data correspondingto Example 2 above is used to illustrate this relationship in Table 6.

TABLE 6 Gasification partial oxidation partial oxidation mol % exitH₂:CO Temperature (° C.) exit H₂:CO CH₄ 1.15 1000 1.25 3.99% 1.15 10501.11 1.13% 1.15 1100 1.06 0.29% 1.15 1150 1.01 0.07% 1.15 1200 0.960.02% 1.15 1250 0.92 0.01% 1.15 1300 0.88 0.00% 1.15 1350 0.84 0.00%1.15 1400 0.81 0.00%

1. A process for the manufacture of a useful product from carbonaceousfeedstock of fluctuating compositional characteristics, the processcomprising the steps of: continuously providing the carbonaceousfeedstock of fluctuating compositional characteristics to a gasificationzone; gasifying the carbonaceous feedstock in the gasification zone toobtain raw synthesis gas; recovering at least part of the raw synthesisgas from the gasification zone and supplying at least part of therecovered raw synthesis gas to a partial oxidation zone; equilibratingthe H₂:CO ratio of the raw synthesis gas in the partial oxidation zoneto obtain equilibrated synthesis gas; recovering at least part of theequilibrated synthesis gas from the partial oxidation zone; optionallyadjusting the H₂:CO ratio of at least part of the equilibrated synthesisgas to obtain adjusted equilibrated synthesis gas; treating theoptionally adjusted equilibrated synthesis gas to remove impurities andgenerate a fine synthesis gas; optionally adjusting the H₂:CO ratio ofat least part of the fine synthesis gas to obtain adjusted finesynthesis gas; and converting the optionally adjusted fine synthesis gasinto the useful product in a further chemical reaction with a particularusage ratio; wherein the fine synthesis gas H₂:CO ratio is below theusage ratio and wherein any optional adjustment of at least part of thefine synthesis gas H₂:CO ratio is effective only to increase the H₂:COratio in the fine synthesis gas to a level at, nearer to or above theusage ratio; wherein the H₂:CO ratio of the raw synthesis gas fluctuatesduring operation of the process as a result of the fluctuatingcompositional characteristics of the carbonaceous feedstock by apercentage of ±x; and the H₂:CO ratio of the equilibrated synthesis gasdoes not fluctuate during operation of the process or fluctuates duringoperation of the process as a result of the fluctuating compositionalcharacteristics of the carbonaceous feedstock by a percentage ±y, ybeing a lower percentage than x.
 2. A process according to claim 1wherein the reaction conditions effective to produce a useful product orthe include a desired feed ratio of H₂:CO and the equilibrated synthesisgas H₂:CO ratio is consistently below that desired feed ratio.
 3. Aprocess according to claim 1 wherein the useful product produced in thereaction corresponds to a certain H₂:CO usage ratio and the equilibratedsynthesis gas H₂:CO ratio is consistently below that usage ratio.
 4. Aprocess according to claim 1 wherein the useful product produced in thereaction corresponds to a certain H₂:CO usage ratio and the optionallyadjusted fine synthesis gas H₂:CO ratio is consistently at or no morethan 20% above or below that usage ratio.
 5. A process according toclaim 1 wherein x is a percentage in the range of from 1 to 300 and y isa percentage in the range of from 0 to
 20. 6. A process according toclaim 1 wherein y is at least 10% lower, at least 25% lower, at least40% lower or at least 50% lower than x.
 7. A process according to claim1 being a continuous process wherein carbonaceous feedstock iscontinuously fed to a gasification zone for gasifying the feedstock. 8.A process according to claim 1 effective to equilibrate the H₂:CO ratioin the raw synthesis gas regardless of the compositional makeup of thecarbonaceous feedstock.
 9. A process according to claim 1 wherein thecarbonaceous feedstock comprises at least one of woody biomass,municipal solid waste and/or commercial and industrial waste.
 10. Aprocess according to claim 1 wherein the step of gasifying thecarbonaceous feedstock comprises gasifying the carbonaceous feedstock inthe presence of steam and oxygen.
 11. A process according to claim 1wherein the raw synthesis gas from the gasification zone has an exittemperature of at least 600° C., of at least 700° C., or of at least800° C.
 12. A process according to claim 1 wherein the partial oxidationzone is non-catalytic.
 13. A process according to claim 1 wherein thepartial oxidation zone operates at a temperature of least 1100° C., atleast 1200° C., or at least 1300° C.
 14. A process according to claim 1wherein the fine synthesis gas is low sulphur containing gas, whereinthe low sulphur containing gas has a sulphur content of less than 0.1ppmv.
 15. A process according to claim 1 wherein at least a portion ofthe optionally adjusted fine synthesis gas is sent to a HydrogenRecovery Unit (HRU), optionally wherein the HRU produces high purityhydrogen, wherein the high purity hydrogen is at least 97%, at least98%, at least 99% pure.
 16. The process according to claim 15 whereinthe high purity hydrogen is used in upstream and/or downstreamprocesses, wherein the high purity hydrogen is at least 97%, at least98%, at least 99% pure.
 17. A process according to claim 1 wherein theprocess further comprises the step of sequentially removing ammoniacal,sulphurous and carbon dioxide impurities from the equilibrated synthesisgas.
 18. A process according to claim 1 wherein the useful product isproduced by subjecting at least part of the optionally adjusted finesynthesis gas to a Fischer-Tropsch conversion.
 19. The process accordingto claim 18 wherein the Fischer-Tropsch conversion is effective toconvert the optionally adjusted fine synthesis gas into liquidhydrocarbons.
 20. The process according to claim 19 wherein the liquidhydrocarbons are upgraded into the useful product.
 21. The processaccording to claim 20 wherein least a part of the liquid hydrocarbonsare upgraded by at least one of hydroprocessing, product fractionation,hydrocracking and/or isomerisation to produce the useful product.
 22. Aprocess according to claim 1 wherein the useful product comprisessynthetic paraffinic kerosene and/or naphtha.
 23. The process accordingto claim 22 wherein the synthetic paraffinic kerosene and/or naphtha isused for transportation fuel or as a gasoline blendstock.